Stents are generally cylindrical-shaped devices that are radially expandable to hold open a segment of a vessel or other anatomical lumen after implantation into the body lumen.
Various types of stents are in use, including expandable and self-expanding stents. Expandable stents generally are conveyed to the area to be treated on balloon catheters or other expandable devices. For insertion, the stent is positioned in a compressed configuration along the delivery device, for example crimped onto a balloon that is folded or otherwise wrapped about a guide wire that is part of the delivery device. After the stent is positioned across the lesion, it is expanded by the delivery device, causing the diameter to expand. For a self-expanding stent, commonly a sheath is retracted, allowing expansion of the stent.
Stents are used in conjunction with balloon catheters in a variety of medical therapeutic applications, including intravascular angioplasty. For example, a balloon catheter device is inflated during percutaneous transluminal coronary angioplasty (PTCA) to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. When inflated, the pressurized balloon exerts a compressive force on the lesion, thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow. Soon after the procedure, however, a significant proportion of treated vessels restenose.
To prevent restenosis, stents, constructed of a metal or polymer, are implanted within the vessel to maintain lumen size. The stent acts as a scaffold to support the lumen in an open position. Configurations of stents include a cylindrical sleeve defined by a mesh, interconnected stents, or like segments. Exemplary stents are disclosed in U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 4,739,762 to Palmaz and U.S. Pat. No. 5,421,955 to Lau.
Stent insertion may cause undesirable reactions such as inflammation, infection, thrombosis, and proliferation of cell growth that occludes the passageway. Stents have been used with coatings to deliver drugs or other therapeutic agents at the site of the stent that may assist in preventing these conditions. In some methods of producing a stent designed to deliver a drug, the drug coating is applied to a stent framework. This may result in the drug being delivered to only those portions of the vessel in direct contact with the stent, providing as little as 20% coverage.
When a graft is used in conjunction with a stent, 100% coverage of the portion of the vessel in direct contact with the graft is possible. The graft component of a stent-graft may also aid in minimizing thrombosis, preventing embolic events, and minimizing contact between the fissured plaque and the hematological elements in the bloodstream.
In addition, the graft component makes the device suitable for use in treating aneurysms. An aneurysm is a bulge or sac that forms in the wall of a blood vessel. The force of normal blood pressure in the aneurysm may cause the vessel to rupture. Aneurysms are most commonly the result of fatty deposits on the vessel wall but may also result from other causes that weaken the vessel wall, including heredity, trauma, or disease.
A number of methods and devices have been developed for treating aneurysms. A standard treatment is surgery, which is performed to replace the section of the vessel where the aneurysm has formed. Some patients are not good candidates for such open surgery, and, due to the highly invasive nature of the open procedure, other patients may not wish to undergo the treatment.
An alternative treatment is a technique known as endovascular stent grafting. In this procedure, a stent-graft is placed inside the vessel affected by the aneurysm in order to reinforce the weakened vessel wall, thereby preventing rupture of the aneurysm. Like stents, stent-grafts are delivered to the area to be treated using balloon catheters or other expandable devices. Certain therapeutic agents may be effective against the formation or progression of aneurysms. Therefore, it may be desirable to use a stent-graft to deliver these therapeutic agents to the site of an aneurysm.
Various methods have been devised to produce stent-grafts. Some of these, such as methods that involve stitching the graft material to the stent, can be labor intensive or may provide inadequate adherence of the graft material to the stent. Other methods may produce devices that cannot deliver the therapeutic agents efficiently. Therefore, it would be desirable to have a stent-graft assembly that overcomes the aforementioned and other disadvantages.